Post-tensioning apparatus for prestressing concrete



K. H. MIDDENDORF 3,270,471

Sept. 6, 1966 POS'I I'ENSVIDNING APPARATUS FOR PRESTRESSING CONCRETEOriginal Filed Nov. 15, 1954 5 Sheets-Sheet 1 INVENTOR. 1 421 M Moon001M- A rog/dry p 1956 K. H. MIDDENDORF 3,270,471

POST-TENSIONING APPARATUS FOR PRESTRESSING CONCRETE Original Filed Nqv.15, 1954 5 Sheets-Sheet 2 I N V EN TOR. fizz 1/ Mmoewooer p 6. 1966 K.H. MIDDENDORF 3,270,471

POST-TENSIONING APPARATUS FOR PRESTRESSING CONCRETE Original Filed Nov.15, 1954 5 Sheets-Sheet 5 INVEN TOR. 1 42! Almom ooef A 'rronA/eY UnitedStates Patent 3,270,471 POST-TENSIONING APPARATUS FOR PRE- STRESSINGCONCRETE Karl H. Middendorf, Costa Mesa, Califi, assignor'to The PresconCorporation, a corporation of Texas Original application Nov. 15, 1954,Ser. No. 468,762. Divided and this application Oct. 10, 1961, Ser. No.144,112

2 Claims. (Cl. 52-223) My invention relates to apparatus forprestressing concrete, and more particularly to a post-tensioningapparatus for prestressing concrete structures. This is a division of myapplication Serial No. 468,762, filed November 15, 1954, onPost-Tensioning Method and Apparatus for Prestressing Mem'bers, nowPatent No. 3,029,490, patented April 17, 1962.

In the art of prestressing concrete, the means that is put under tensionto accomplish the prestressing of the concrete is commonly referred toas a tendon. Such a tendon is normally composed of three parts: twoends, either stressing or dead end anchors or couplers and a hightensile strength element of varying length between the ends of saidtendon. These high tensile elements may be made up of wires, bars orwire strands.

In my improved apparatus for post-tensioning concrete prestressingmembers, the tendons comprise a plurality of wires that are providedwith clips at predetermined spaced intervals along the length thereoffor holding the tension members in proper relative relationship to eachother. In the form of tendon shown in the drawings, said clips hold saidwires in spaced side by side relation in a row transversely of thelength of the tension members, thus producing what is commonly referredto as a fiat tendon, that is, one that is of greater width thanthickness.

I provide a plurality of clips that are of such a character that thetension members are kept in desired relative position, but which willonly slightly grip the tension members so that the same can be readilyshifted or slid longitudinally through the clips, said clips spacing thetension members transversely of the length thereof. Preferably saidclips are indented between the Wires, to space the same from each otherand slightly grip them. I Said .clips hold the wires alignedtransversely of the tendon so as to maintain the same in a side by sidespaced relation.

It is another purpose of my invention to provide a bearing and spacingplate at each end of the member that is to be prestressed for arrangingthe ends of the wires or other tension members so that there issufficient concrete surrounding each wire at a predetermined distanceinwardly from the base of the plate to eliminate any excessive pressureon the concrete. 50

It is a further purpose of my invention to provide new and improvedstressing units that are in the form of blocklike members, which may beeither threaded to engage with a suitable threaded fitting on a jack orother stressing device, or which are provided with smooth inclined facesto be gripped by the jack so as to not slip relative thereto. Anadvantage of the latter type of stressing unit is that this type can bemade of cast material and can be made in the form of a strip or bar forstressing a group of the tension members instead of individuallystressing the same, if this should be desired.

Other objects and advantages of my invention will appear as thedescription of the drawings proceeds. I desire to have it understood,however, that I do not intend to limit myself to the particular detailsshown or described, except as defined in the claims.

In the drawings:

FIG. 1 is a view in side elevation of a concrete structural member madein accordance with my invention.

FIG. 2 is a fragmentary vertical sectional view on an enlarged scalethrough the same at one end thereof.

FIG. 3 is a view similar to FIG. 2 of a modification.

FIG. 4 is a fragmentary vertical sectional view on an enlarged scalethrough the opposite end portions of the structural member shown in FIG.1, the mid-portion thereof being broken away, showing the parts in theposition which the same would assume in the second step of my method.

FIG. 5 is a horizontal sectional view through a fragmentary portion ofthe stressing means and a fragmentary portion of a structural member towhich my invention is applied, with the stressing means in engagementwith the right hand end of one of the structural members shown in FIG.4.

FIG. 6 is a transverse sectional view on a further enlarged scalethrough one of the spacing members and the tension members associatedtherewith.

FIG. 7 is a plan view of the spacing mem'ber, showing fragmentaryportions of the tension members spaced thereb FIG. 8 is an end elevationof a structural member, showing the form of the invention illustrated inFIG. 3.

FIG. 9 is an enlarged cross sectional view through one of the stressingmembers shown in FIGS. 2, 3 and 4.

FIG. 10 is a similar view of a modified form of stressing member.

FIG. 11 is an end elevation of the stressing member shown in FIG. 10.

FIG. 12 is a view similar to FIG. 8 of a structural member, showing theform of stressing member illustrated in FIGS. 10 and 11.

FIG. 13 is a similar view, showing a further modified form of stressingmember.

FIG. 14 is a vertical sectional view through the stressing member shownin FIG. 13, on an enlarged scale, and

FIG. 15 is a view similar to FIG. 5, showing a modified form ofstressing means for cooperation with a modified form of stressing memberthat is not threaded.

Referring in detail to the drawings, in FIG. 1 a structural member 20,which may be a beam and which has a concrete body portion, is shown ashaving a plurality of tension members 21 embedded therein, such aswires, that can be put under tensile stress to prestress the structuralmember 20. A spacing and bearing plate 22 is provided in each end of thestructural member through which the members 21 pass, and in FIG. 1 saidmembers are shown as being provided with spacing means 23 at each endthereof between said plates 22 and stressing members 24, the position ofthe parts shown in FIG. 1 being that of the finished prestressed beamwith the tension members 21 under the full tensile stress to which theseare to be put to get the desired prestressing of the member 20. Thespacing means 23 may be of any desired character such as shown in eitherFIG. 2 or FIG. 3 and the stressing members or anchors 24 may be ofvarious types as well be described below.

In FIG. 2 a fragmentary portion of one end of such a structural memberas shown in FIG. 1 is shown, in which the members 21 are shown as beingheld in a predetermined spaced relation by means of the bearing plate22, which has openings therein at 25 through which said tension memberspass. Thus the tension members 21 are arranged in spaced relation in thebody of concrete 26. Each of said tension members, which are preferablyin the form of wires of high tensile strength, are provided with heads27 that are formed thereon from the material of the wire. Ascrew-threaded block 28 serves as a stressing or anchor member for eachof said tension members 21, there being an opening 29 centrally througheach of said members 28 (see FIG. 9) and said member 28 being externallyscrew-threaded as indicated at 30 in the drawings.

In assembling the structure shown in FIG. 1, a plurality of clips,constituting clamping means for holding the tension members in side byside spaced relation are arranged at desired intervals lengthwise of thetension members 21, said clips being indicated by the numeral 31 inFIG. 1. The details of construction of said clips are shown in FIGS. 6and 7. Each of said clips is made up of a pair of sheet metal members 32and 33, which are each provided with a portion 34, which is reduced inwidth and which is adapted to be bent around the end edge 35 of theopposite end of the member cooperating therewith, as shown at 36 inFIGS. 6 and 7, to clamp the members 32 and 33 to each other. In FIG. 6the reduced portion 34 is shown in the position that it has before beingcrimped over into holding position at the left of said figure, and inits crimped over position of holding position at the right thereof. Thelength of the clips and thus of the portions 32 and 33 thereof isdependent upon the number of tension members that are spaced thereby,the number shown in FIGS. 6 and 7 being a relatively small number oftension members that would be so connected together in transversealignment by said clips in practice.

The clips are provided with indentations 37 that are opposite each otherso as to provide adjacent portions 33 in the opposite members 32 and 33of said clips for spacing the transversely aligned wires 21 from eachother, said clips thus constituting spacing members for said wires. Saidmembers 32 and 33 are bent toward each other at 39 adjacent the endportions 35 and reduced portions 34 to thus form pockets in which thetension members 21 are located and from which these can not move towardor away from each other when the tongues 34 are crimped around the endedges 35 in the position shown at 36 in FIGS. 6 and 7. However, thetension members 21 are not gripped tightly enough by the spacing membersto prevent sliding of the tension members 21 through the spacing memberslengthwise of said tension members 21.

Said tension members 21 are placed in the desired position in the formwith the spacing members 31 provided thereon at the desired points alongthe length thereof to obtain the desired transverse alignment thereofand the spacing plates 22 are placed in the desired position in theform. The spacing plates 22 and the stressing members 24 are placed onthe tension members 21 before the heads 27 are formed thereon. When thetension members 21 are placed in position in the form the stressingmembers, such as the members 28 shown in FIG. 2, are put in positionadjacent the heads 27, and U-shaped spacing members 10 are placed inposition between the members 28 and the plate 22, said spacing membersbeing of such size that this will place the members 28 at the other endsof the tension members 21 in position against the plate 22 at the otherend of the structural member that is to be prestressed.

The concrete is then poured and after it has been allowed to set asuflicient time to permit movement of the tension members 21longitudinally of themselves therein without damage to the structuralmember the tension members 21 are shifted lengthwise of themselves inthe concrete body portion. To do this the spacing members 44 are removedfrom the end of the tension members to which these have been applied,which is the left hand end as shown in FIG. 2, and the tensioning orstressing means is applied to the other end of the tension members 21,for example, in the manner illustrated in FIG. 5, at the right hand endof said members. The stressing or tension applying means is shown asbeing a movable member 41 of a jack having a body portion 42 thatengages the plate 22 at the right hand end of the structural member 20.Said jack may be of any desired or well known character and is providedwith a suitable internally screw-threaded portion 43 that isscrew-threadedly engaged by the threads 30 on the member 23. Obviouslythe tensioning is accomplished by moving the member 41 to the rightrelative to the member 42 as viewed in FIG. 5. The movement of the partsis only sufficient to move the member 28 on the member 21 at theopposite end or left hand end of said structural member 20 intoengagement with the plate 22 at that end thereof.

If desired spacing members 40 can then be inserted between the anchormembers 23 and the bearing plate 22 at the right hand end of thestructural member as viewed in FIG. 1, or the tensioning means, afterhaving moved the tension members 21 all to the right longitudinally ofthemselves in the manner above described, can be engaged With themembers 28 on tie tension members 21 at the opposite or left hand end ofthe structural member to again move the tension members 21 lengthwise ofthemselves in the concrete body portion of the structural member 20 andthis can be repeated alternately at opposite ends of the tension members21 as often as may be necessary to break any bond that might existbetween the tension members and the concrete body portion to permitmovement thereof longitudinally for the purpose of tensioning saidmembers 21 when the post-tensioning thereof for prestressing theconcrete structural member 20 is to be performed. This is not done untilthe concrete of the structural member has been cured sufiiciently toreach its maximum strength, whereupon the posttensioning is completed byapplying the tensioning means first to one end of the structural members21 and inserting spacing members 23 between the stressing members 28 andthe plate 22 at that end of the structural members, then tensioning themembers 21 at the other end thereof to the desired amount and placingspacing means 23 between said members 28 and the plate 22 at the lastmentioned end of said structural member, completing the prestressing.

During the shifting of the tension members 21 lengthwise of themselvesthe clips 31 hold these in properly spaced side by side relationtransversely of the structural member 2th and the plate 22 will hold thesame in properly spread out relation at the ends thereof in thestructural member, but neither of the spacing members in any mannerinterferes with the longitudinal shifting of the tension members 21.

Instead of using a separate U-shaped spacing member 49 between each ofthe stressing or anchor members 28 and the bearing plate 22 adjacent thesame as shown in FIG. 2, a single U-shaped spacing member as for a groupof said members 28 may be provided, as shown in FIG. 3. The member 1this also shown as being applied to the structure to space the members 28from the bearing plate 22 in FIG. 8. The members 40 are provided with abend at 4% connecting a pair of parallel legs 45, thus forming aU-shaped member. The members 40 are similarly made, but the leg portionsare shorter, as will be obvious from FIG. 2. Said U-shaped spacingmembers 46 or 40 can be very readily inserted between the anchor members28 and the bearing plate 22 while the tensioning means comprising themembers 41 and 42 are in position, as shown in FIG. 5, by passing thesame between the bearing plate 22 and the anchor member 28 through thespace 4-6, as the body portion 4-2 has openings therein between thespaced legs 47 provided thereon.

In FIG. 4 the structural member is shown after the tension members 21have been shifted lengthwise of themselves from the position shown inFIG. 2 and a spacing member 40 has been inserted between the stressingor anchor members 28 at the right hand end of said tension members 21and the bearing plate 22. With the member 46 in the position shown inFIG. 4, or members 40 such as shown in FIG. 2, in such a position, thetensioning means can be applied to the stressing or anchor member 28 atthe left hand end of the tension members 21 as shown in FIG. 4 until thedesired tension has been placed on each thereof to prestress theconcrete to the desired amount. Then a spacing member 40' or a pluralityof spacing members 48', can be inserted between the anchor members 23and the bearing member 22 at the left hand end of the structural member,as viewed in FIG. 4. This is the condition of the structural memberillustrated in FIG. 1. This last step is, of course, not taken until theconcrete body portion 26 has reached its maximum strength. The spacingmembers 40 or 40' are made of greater thickness between the two oppositeedges thereof that are in engagement with the members 28 and 22 than thethickness of the material from which they are made, which, however, isof sufficiently heavy gauge that it will withstand the compression thatis exerted on the spacing member in use.

Instead of providing a screw-threaded stressing or anchor member, suchas the member 28, a stressing or anchor member that is of a taperingcharacter may be provided, as illustrated in FIGS. and 11. Saidstressing or anchor member 48 has a body portion 49 that tapers towardthe end 50 thereof and has a central opening 51 therein for the tensionmember 21. The one pair of opposite side faces 52 thereof taper from thelarger end 53 thereof to the smaller end 50 thereof uniformly, thusforming a wedge-like body portion for the stressing or anchor member.The faces of the member 48 that extend perpendicularly to the faces 52are perpendicular to the ends 50 and 53 of the member 48, these facesbeing indicated by the numeral 54 in FIG. 11. Said stressing or anchormembers 48 are shown in position on the members 21 with the heads 27thereof in engagement with the larger ends 53 thereof in FIG. 12, and aU-shaped spacing member 40 is shown as being in position between saidanchor members 48 and the bearing plate 22.

If desired, instead of using a plurality of stressing or .anchor members48, a single stressing or anchor bar 48' can be used, which is providedwith inclined or tapering sides 52' corresponding to the faces 52 of themember 48, and is provided with a plurality of openings 51 for tensionmembers 21, said member 48 being of a bar-like character as shown so asto receive a plurality of vertically aligned tension members 21 in themanner illustrated in FIG. 13. In the use of such a stressing or anchormember as the member 48 or the member 48', the jack has to be modifiedto provide a movable member 41' that has inclined walls 55 with whichthe inclined walls 52 or 52 of the members 48 or 48' engage to providefor movement of the stressing member 48 or 48 by means of the jack. Thejack is otherwise constructed in the same manner as that used for thethreaded members 28, as illustrated in FIG. 5.

An advantage in using a stressing or anchor member such as the member 48or the member 48 is that it can be made by casting without any finishingbeing required, instead of having a member, such as the member 28, thathas to be threaded.

What I claim is:

1. A post-tensioned prestressed concrete structural member having aconcrete body portion having a fiat bottom face, an elongatedprestressing tendon for said concrete body portion embedded thereinhaving a transversely flat body portion consisting of a plurality ofclosely transversely adjacent high tensile strength steel wiresextending in parallelism longitudinally of said tendon and means forholding said wires in a single straight row in close side by sideadjacency with said row extending transversely of said tendon parallelto the bottom face of said concrete body portion, consisting of clampingmeans frictionally gripping said wires adjacent opposite ends of saidmain body portion of said tendon and at longitudinally spaced intervalsalong the same therebetween, each of said clamping means consisting ofduplicate paired sheet metal members, one member of each pair extendingtransversely across said wires in engagement therewith on one sidethereof and the other member of each pair extending transversely acrosssaid wires in engagement therewith on the other side thereof, saidpaired members having means for holding the same assembled with saidwires to connect said wires slidably with said clamping means formovement of said wires relative to said clamping means longitudinally ofsaid wires independently of each other.

2. A post-tensioned prestressed concrete structural member having anelongated concrete body portion having a flat bottom face, aprestressing tendon for said concrete body portion embedded thereinhaving a transversely fiat body portion consisting of a plurality ofclosely transversely adjacent high tensile strength steel wiresextending in parallelism longitudinally of said tendon and means forholding said wires in a single straight row in close side by sideadjacency with said row extending transversely of said tendon parallelto the bottom face of said concrete body portion, consisting of clampingmeans frictionally gripping said wires adjacent opposite ends of saidmain body portion of said tendon and at longitudinally spaced intervalsalong the same therebetween, each of said clamping means consisting ofduplicate paired sheet metal members, one member of each pair extendingtransversely across said wires in engagement therewith on one sidethereof and the other member of each pair extending transversely acrosssaid wires in engagement therewith on the other side thereof, saidmembers having interengaging marginal portions at opposite ends thereofholding said members in frictional engagement with said wires to connectsaid wires slidably with said clamping means for movement of said wiresrelative to said clamping means longitudinally of said wiresindependently of each other, and indentations on said sheet metalmembers extending between said wires to space the same.

References Cited by the Examiner UNITED STATES PATENTS 756,309 4/1904Wight 52723 778,416 12/1904 Kyle 52648 875,396 12/1907 White 52708960,305 6/1910 Gilbreth 52723 977,345 11/1910 Tidnam et al. 251311,001,462 8/1911 Scott 52648 1.073,931 9/1913 Royse 52693 1,304,8155/1919 Sharp 52712 1,608,184 11/1926 Rumble 52220 X 2,404,531 7 1946Robertson 24868 2,425,033 8/ 1947 Fletcher 24868 2,637,895 5/1953 Blaton52228 X 2,675,695 4/1954 Coif 52225 2,804,674 9/1955 Long 52223 X2,941,394 6/1960 Brandt 52223 2,988,794 6/1961 Gutt 52223 X FOREIGNPATENTS 183,214 9/1955 Austria.

489,515 l/1953 Canada.

345,491 10/ 1904 France. 1,223,043 1/ 1960 France.

739,480 10/1955 Great Britain.

FRANK L. ABBOTT, Primary Examiner.

WILLIAM I. MUSHAKE, HENRY C. SUTHERLAND,

RICHARD W. COOKE, JR., Examiners.

JACOB L. NACKENOFF, J. L. RIDGILL,

. Assistant Examiners.

1. A POST-TENSIONED PRESTRESSED CONCRETE STRUCTURAL MEMBER HAVING ACONCRETE BODY PORTION HAVING A FLAT BOTTOM FACE, AN ELONGATEDPRESTRESSING TENDON FOR SAID CONCRETE BODY PORTION EMBEDDED THEREINHAVING A TRANSVERSELY FLAT BODY PORTION CONSISTING OF A PLURALITY OFCLOSELY TRANSVERSELY ADJACENT HIGH TENSILE STRENGTH STEEL WIRESEXTENDING IN PARALLELISM LONGITUDINALLY OF SAID TENDON AND MEANS FORHOLDING SAID WIRES IN A SINGLE STRAIGHT ROW IN CLOSE SIDE BY SIDEADDJACENCY WITH SAID ROW EXTENDING TRANSVERSELY OF SAID TENDON PARALLELTO THE BOTTOM FACE OF SAID CONCRETE BODY PORTION, CONSISTING OF CLAMPINGMEANS FRICTIONALLY GRIPPING SAID WIRES ADJACENT OPPOSITE ENDS OF SAIDMAIN BODY PORTION OF SAID TENDON AND AT LONGITUDINALLY SPACED INTERVALSALONG THE SAME THEREBETWEEN, EACH OF SAID CLAMPING MEANS CONSISTING OFDUPLICATE PAIRED SHEET METAL MEMBERS, ONE MEMBER OF EACH PAIR EXTENDINGTRANSVERSELY ACROSS SAID WIRES IN ENGAGEMENT THEREWITH ON ONE SIDETHEREOF AND THE OTHER MEMBER OF EACH PAIR EXTENDING TRANSVERSELY ACROSSSAID WIRES IN ENGAGEMENT THEREWITH ON THE OTHER SIDE THEREOF, SAIDPAIRED MEMBERS HAVING MEANS FOR HOLDING THE SAME ASSEMBLED WITH SAIDWIRES TO CONNECT SAID WIRES SLIDABLY WITH SAID CLAMPING MEANS FORMOVEMENT OF SAID WIRES RELATIVE TO SAID CLAMPING MEANS LONGITUDINALLY OFSAID WIRES INDEPENDENTLY OF EACH OTHER.